Method and apparatus for orienting arrays of mechanically linked heliostats for focusing the incident sunlight on a stationary object

Abstract

The present invention is a method and apparatus for periodic orientation of arrays of mechanically linked heliostats positioned on rotatable shafts such that incident sunlight is focused on a stationary object. In each altitudinal orientation a minuscule predefined push is given by an actuator and the time interval between each altitudinal orientation is 2×(T 2 −T 1 )/n. For azimuthal reorientation, the magnitude of rotation of rotatable shafts is determined by (Y×Sin γ)/2 degrees, and as per the position of the sun in the sky, the determined magnitude in degrees is added/subtracted to form angle θ′. The length ‘C’ of the linear actuator with its arm at angle θ can be extended/retracted to length ‘C 1 ’ such that angle θ′ is achieved, wherein an arm affixed with each rotatable shaft and coupled with a linear actuator provides the ability to rotate the rotatable shaft in clockwise or anticlockwise direction.

We claim: 
     
         1 . A method for synchronous orientation of mechanically-linked heliostats to focus incident sunlight onto a central receiver, said method comprising:
 a) dividing the sky into four imaginary quadrants A, B, C and D via imaginary east-west line (from 90° azimuth to 270° azimuth) and north-south line (from 0° azimuth to 180° azimuth) bisecting at the zenith to form a three-dimensional grid for mapping altitudinal and azimuthal trajectory of the sun across the sky with help of a common art solar position calculation program/software;   b) mapping position of the sun and upon occurrence of a first predefined event, recording corresponding time (T 1 ) as start point;   c) mapping position of the sun and upon occurrence of a second predefined event, recording the corresponding time (T 2 ) as mid point;   d) determining altitudinal (elevational) displacement of the sun to occasion suitable means to introduce a calibrated compensation in heliostat orientation necessary to focus sunlight onto said central receiver;   e) determining azimuthal displacement of the sun to occasion suitable means to introduce a calibrated compensation in heliostat orientation necessary to focus sunlight onto said central receiver;   f) repeating steps a to e for continued synchronous orientation of mechanically linked heliostats to continuously focus sunlight onto said central receiver.   
     
     
         2 . The method of  claim 1 , wherein the sun elevation, and sun azimuth, values are periodically monitored at intervals ranging from 30 seconds to 1800 seconds using said common art solar position calculation program/software. 
     
     
         3 . The method of  claim 1 , wherein said first predefined event is said to occur upon reaching a user-defined eastern sun elevation in degrees like 30° eastern sun elevation. 
     
     
         4 . The method of  claim 1 , wherein said second predefined event indicative of the sun azimuth being 180° or 360°. 
     
     
         5 . The method of  claim 1 , wherein determination of apparent angular displacement γ of the sun with respect to said east west line passing through the zenith is calculated by the formula [90°−azimuth value of the sun] when the sun is observed to be present in quadrant A, which quadrant A is present in the north east region of the sky. 
     
     
         6 . The method of  claim 1 , wherein determination of apparent angular displacement γ of the sun with respect to said east west line passing through the zenith is calculated by the formula [azimuth value of the sun−90°] when the sun is observed to be present in quadrant B, which quadrant B is present in south east region of the sky. 
     
     
         7 . The method of  claim 1 , wherein determination of apparent angular displacement γ of the sun with respect to said east west line passing through the zenith is calculated by the formula [270°−azimuth value of the sun] when the sun is observed to be present in quadrant C, which quadrant C is present in south west region of the sky. 
     
     
         8 . The method of  claim 1 , wherein determination of apparent angular displacement γ of the sun with respect to said east west line passing through the zenith is calculated by the formula [azimuth value of the sun−270°] when the sun is observed to be present in quadrant D, which quadrant D is present in northwest region of the sky. 
     
     
         9 . The method of  claim 1 , wherein said means to introduce a calibrated compensation in heliostat orientation according to apparent altitudinal displacement of the sun is an actuator like a linear stepper motor actuator with a pusher ball nut and lead screw in operational linkage to said heliostats, wherein displaceable said pusher ball nut travels on said lead screw for actuating a pusher rod for rotating said heliostats from a mirror elevation of predefined degrees eastern to a mirror elevation of predefined degrees western orientation. 
     
     
         10 . The method of  claim 9 , wherein actuation periodicity of the said actuator for achieving orientation of heliostats necessary to focus sunlight onto said central receiver is calculated by the formula 2(T 2 −T 1 )/n where n is the number of consecutive altitudinal orientations of said heliostats required in a day necessary to track the sun from a predefined degrees of solar elevation like 30° eastern in the morning to a predefined degrees of solar elevation like 30° western in the evening. 
     
     
         11 . The method of  claim 10 , wherein said n number of altitudinal orientations of the said heliostats required in a day necessary to track the sun from predefined degrees of solar elevation (eastern) in the morning to predefined degrees of solar elevation (western) in the evening depends on total length of said lead screw on which said displaceable pusher ball nut travels for actuating said pusher rod for rotating said heliostats, pitch of the said lead screw, and number of steps that said stepper motor rotates in each altitudinal orientation. 
     
     
         12 . The method of  claim 1 , wherein said means to introduce a calibrated compensation in heliostat orientation according to apparent azimuthal displacement of the sun is an east west directional rotatable shaft in operational linkage to said heliostats and further characterized in having a central/distal arm affixed with said rotatable shaft and coupled with a drive means providing ability to rotate said rotatable shaft in both clockwise and anticlockwise directions. 
     
     
         13 . The method of  claim 12 , wherein actuation periodicity of the rotatable shaft for achieving orientation of heliostats necessary to focus sunlight onto said central receiver is calculated by the formula 2(T 2 −T 1 )/p where p is a user defined arbitrary time unit, and wherein said formula 2(T 2 −T 1 )/p gives total number of azimuthal orientations required in a functional day. 
     
     
         14 . The method of  claim 12 , wherein magnitude of rotation of said rotatable shaft necessary to focus sunlight onto said central receiver is calculated by the formula (Y×Sin γ)/2 degrees, wherein Y is ‘90°−sun elevation in degrees’. 
     
     
         15 . The method of  claim 12 , wherein direction of rotation of the said rotational shaft depends on whether it is the start of operations or not the start of operations. 
     
     
         16 . The method of  claim 12 , wherein at the start of the operation, direction of rotation of the said rotational shaft is northward when sun lies in the quadrant A at that instant, and direction of rotation of the said rotational shaft is southward when sun lies in the quadrant B at that instant. 
     
     
         17 . The method of  claim 12 , wherein, in northern hemisphere, direction of rotation of the said rotational shaft is southward when the sun azimuth is ≦180° and it is not start of the operation. 
     
     
         18 . The method of  claim 15 , wherein in northern hemisphere, direction of rotation of the said rotational shaft is northward when sun azimuth is >180° and it is not start of the operations. 
     
     
         19 . The method of  claim 1 , wherein accumulated mechanical error is negated by readjusting the altitudinal and azimuthal status after every 120 minutes whereupon functionality extremes of the heliostat orientation means are force-achieved via control check-loop. 
     
     
         20 . An apparatus for orienting arrays of mechanically linked heliostats for focusing the incident sunlight on a stationary object, said apparatus comprising:
 a) a computer executable software code housed in suitable computer readable medium for embodying method of  claim 1 ;   b) a central processing unit (CPU) means to execute said software code for generating controlling commands for actuator/s for rotating pivotably rotatable mounts of heliostats located on related rotatable shafts for tracking an apparent altitudinal motion of the sun in the sky, and for generating controlling commands for actuator/s for rotating related rotatable shafts for tracking an apparent azimuthal motion of the sun in the sky;   c) a display means for alphanumerical display of user information like time, date, system status, controlling commands;   c) a real time clock for supplying time data to be used to control the time related parameters in method of  claim 1 ;   d) input means for interacting with application software or entering data like time data or Geographical location data;   e) input/output port for exchange of data with other devices;   f) Mechanical linkage as illustrated in the accompanying figure for orienting arrays of mechanically linked heliostats for focusing the incident sunlight on a stationary object.